The conventional industrial hydrogenation of dinitrotoluene, (dinitrotoluene), to toluenediamine, (toluenediamine), has been accomplished in a continuous three phase slurry stirred tank reactor. Dinitrotoluene is introduced in the stirred reactor along with a solvent such as methanol at a concentration of from 5 to 15 gram moles/m.sup.3. Finely divided powder catalysts, especially nickel and palladium based catalysts, are suspended in the liquid phase stirred tank reactor and used as the primary catalysts to effect hydrogenation of the dinitrotoluene. Unfortunately, the use of these types of catalytic processes in the hydrogenation of dinitrotoluene result in processing difficulties, safety concerns, hygiene issues and environmental problems.
An option to the use of finely divided powder catalysts in stirred reactors has been the use of pelleted catalysts in fixed bed reactors. While this reactor technology does eliminate much of the handling and waste problems, a number of engineering challenges has not permitted the application of fixed bed reactor technology to the hydrogenation of nitroaromatic compounds in general and dinitrotoluene hydrogenation in particular. Controlling the overall temperature rise and temperature gradients in the reaction process, particularly in a dinitrotoluene process, has been one problem. Nitroaromatic compounds release more that 500 kJ/mole per nitro-functional group during hydrogenation. A second problem is that in fixed bed packed reactors there is a significant pressure drop due to the high flow rates required for nitroaromatic hydrogenation. A third problem is that liquid-gas distribution is problematic thus often leading to poor conversion and localized concentration gradients. These problems are cumulative in the production process and contribute to the considerable safety issues present in dinitrotoluene hydrogenation.
High void volume reactors incorporating monolith catalysts have been used in laboratory scale chemical processes including hydrogenation of nitroaromatics such as nitrobenzoic acid and m-nitrotoluene. These reactors have been operated at low conversion per pass with continuous recycle, thus simulating a batch process.
The following articles and patents are representative of catalytic processes employing monolith catalysts and processes in chemical reactions including the hydrogenation of nitroaromatics and other organic compounds.
Hatziantoniou, et al. in "The Segmented Two-Phase Flow Monolithic Catalyst Reactor. An Alternative for Liquid-Phase Hydrogenations,", Ind. Eng. Chem. Fundam., Vol. 23, No.1, 82-88 (1984) discloses the liquid phase hydrogenation of nitrobenzoic acid (NBA) to aminobenzoic acid (ABA) in the presence of a solid palladium monolithic catalyst. The monolithic catalyst consisted of a number of parallel plates separated from each other by corrugated planes forming a system of parallel channels having a cross sectional area of 1 mm.sup.2 per channel. The composition of the monolith comprised a mixture of glass, silica, alumina, and minor amounts of other oxides reinforced by asbestos fibers with palladium metal incorporated into the monolith in an amount of 2.5% palladium by weight. The reactor system was operated as a simulated, isothermal batch process. Feed concentrations between 50 and 100 moles/m.sup.3 were cycled through the reactor with less than 10% conversion per pass until the final conversion was between 50% and 98%
Hatziantoniou, et al. in "Mass Transfer and Selectivity in Liquid-Phase Hydrogenation of Nitro Compounds in a Monolithic Catalyst Reactor with Segmented Gas-Liquid Flow", Ind. Eng. Chem. Process Des. Dev., Vol. 25, No.4, 964-970 (1986) discloses the isothermal hydrogenation of nitrobenzene and m-nitrotoluene in a monolithic catalyst impregnated with palladium. The authors report that the activity of the catalyst is high and therefore mass-transfer is rate determining. Hydrogenation was carried out at 590 and 980 kPa at temperatures of 73.degree. and 103.degree. C. Again, less than 10% conversion per pass was achieved.
U.S. Pat. No. 4,520,124 discloses a process for producing catalytic structures in the form of sheets or honeycombs for the gas phase reduction of nitrogen oxides. A porous honeycomb structure is impregnated with titanium dioxide as a carrier material. The structure then is immersed in a solution containing a catalytically active oxide of copper, iron, vanadium, tungsten or molybdenum and then calcined to form the catalyst. Gas phase reduction of nitrogen oxides was effected in the presence of ammonia as a reducing agent.
U.S. Pat. No. 4,743,577 discloses metallic catalysts which are extended as thin surface layers upon a porous, sintered metal substrate for use in hydrogenation and decarbonylation reactions. In forming a monolith, a first active catalytic material, such as palladium, is extended as a thin metallic layer upon a surface of a second metal present in the form of porous, sintered substrate and the resulting catalyst used for hydrogenation, deoxygenation and other chemical reactions. The monolithic metal catalyst incorporates such catalytic materials such as palladium, nickel and rhodium, as well as platinum, copper, ruthenium, cobalt and mixtures. Support metals include titanium, zirconium, tungsten, chromium, nickel and alloys.
U.S. Pat. No. 5,250,490 discloses a catalyst made by an electrolysis process for use in a variety of chemical reactions such as hydrogenation, deamination, amination and so forth. The catalyst is comprised of a noble metal deposited, or fixed in place, on a base metal, the base metal being in form of sheets, wire gauze, spiral windirigs and so forth. The preferred base metal is steel which has a low surface area, e.g., less than 1 square meter per gram of material. Catalytic metals which can be used to form the catalysts include platinum, rhodium, ruthenium, palladium, iridium and the like.
U.S. Pat. No. 4,400,538 discloses the fixed bed catalytic hydrogenation of mononitrobenzene and dinitrobenzene in a stirred autoclave. The catalyst is an activated noble metal, e.g., palladium, iridium, rhodium, ruthenium or platinum and is in the form of a screen or coherent body such as perforated or fluted sheets, honeycomb structure, foils, wires, etc. Temperatures range from .about.130.degree. to 150.degree. C.
U.S. Pat. No. 3,356,728 discloses the catalytic hydrogenation of aromatic polynitro compounds to aromatic polyamines via a slurry-phase catalyst system. Finely defined Raney nickel is the preferred catalyst.
U.S. Pat. No. 2,976,320 discloses a process for producing toluenediamine by the catalytic hydrogenation of dinitrotoluene utilizing an aqueous suspension of a palladium or platinum as the catalyst. The dinitro compound is dissolved in methanol.